Most of the modern polarimetric weather radars provide the option of measuring linear depolarization ratio or “LDR.” Historically, it was the first polarimetric variable measured by polarimetric weather radars and it was primarily utilized for hail detection and discrimination between rain and snow. For example, in the radar S-band frequencies for rain LDR is less than −25 dB, but is much higher for hail, melting snow, and non-meteorological scattering objects and atmospheric conditions.
In the LDR mode of operation, the waves with horizontal polarization are transmitted and the waves with both horizontal (“H”) and vertical (“V”) polarizations are received. In polarimetric radars utilizing the simultaneous transmission and reception of H and V waves (i.e. an “SHV” mode of operation) the differential reflectivity “ZDR,” differential phase ΦDP, and cross-correlation coefficients ρhv may be measured. These variables are not practically measurable in an LDR mode of operation, and hence is one of the disadvantages of using an LDR mode of operation in polarimetric weather radars.
Another limitation in using an LDR mode of operation in polarimetric weather radars is the need to have a relatively high signal to noise ratio in order to effectively process reflectivity data from an LDR radar transmission. For example, a signal to noise ratio of at least 25-30 dB is required in order to make use of LDR in order to recognize objects of interest in the reflectivity data. Consequently, use of an LDR mode of operation is considered as a secondary mode of operation and is currently not widely used for operational applications, nor even accommodated in some configurations of polarimetric weather radars.
Other advantages of using CDR as opposed to LDR include receiving higher power magnitudes in reflectivity data so that CDR can be more reliably measured over larger areas and experiencing less ambiguity in meteorological interpretation because CDR is not affected by the orientation of atmospheric particles during transmission.
Hence, what is needed is a system that can estimate CDR in the linear polarization basis in addition to standard radar polarimetric radar variables commonly measured by operational weather radars, and to do so without affecting those data results by propagation effects.